“…For the plastic zone of thin film coatings, the power law constitutive equation is considered in most investigations, since it is the most applicable rule of plastic behavior for most materials, especially metals. 12 With the assumption of a zero interception curve, as shown in Figure 7, the power law relation can be written according to Holloman's equation where ɛr, B , and n are the representative strain, strain hardening strength, and strain hardening exponent, respectively. When the continuity condition is applied to the above equation, the constant B can be obtained as Figure 7.Schematic representation of the stress–strain diagram for elastic-plastic behavior in the power law general form with zero intercept.…”
Section: Materials Behaviormentioning
confidence: 99%
“…10 Most of the other methods are based on a comprehensive investigation of the parameters affecting the indentation curves during finite element method (FEM) simulations. 12,13 Parallel methods, mainly numerical approaches are usually applied to simulate material's real status. This concept proposes a kind of method that extracts the required material properties through comparison of the conditions which generate similar results by both experimental and numerical approaches.…”
Obtaining the plastic properties of thin film coatings has been the main challenge for decades. Implementing the hybrid methods seems to be an applicable way to address this issue. Unfortunately, limitations of nonunique answers together with the need for enormous amount of calculations are counted as the main challenges. To overcome such difficulties, a modified dimensional analysis method is proposed, which is able to reduce the number of dimensionless parameters. Another novel algorithm named “minimum resultant error method” is developed to provide proper criteria to investigate the compliance of the analytical results with empirical data. With this algorithm, yield stress, strain hardening exponent, and strain hardening coefficient are extracted as unique values by using a single indenter nanoindentation results. The simulation results are processed with combined modified dimensional analysis method and minimum resultant error method algorithms. The effects of interlayer, friction coefficient, and indenter tip radius are investigated. Error analysis to the modulus of elasticity is undertaken and the results show less than 2% error for the infimum point, while the individual dimensionless functions errors are below 3.4%. According to the results, this new approach is well-coped with the earlier studies.
“…For the plastic zone of thin film coatings, the power law constitutive equation is considered in most investigations, since it is the most applicable rule of plastic behavior for most materials, especially metals. 12 With the assumption of a zero interception curve, as shown in Figure 7, the power law relation can be written according to Holloman's equation where ɛr, B , and n are the representative strain, strain hardening strength, and strain hardening exponent, respectively. When the continuity condition is applied to the above equation, the constant B can be obtained as Figure 7.Schematic representation of the stress–strain diagram for elastic-plastic behavior in the power law general form with zero intercept.…”
Section: Materials Behaviormentioning
confidence: 99%
“…10 Most of the other methods are based on a comprehensive investigation of the parameters affecting the indentation curves during finite element method (FEM) simulations. 12,13 Parallel methods, mainly numerical approaches are usually applied to simulate material's real status. This concept proposes a kind of method that extracts the required material properties through comparison of the conditions which generate similar results by both experimental and numerical approaches.…”
Obtaining the plastic properties of thin film coatings has been the main challenge for decades. Implementing the hybrid methods seems to be an applicable way to address this issue. Unfortunately, limitations of nonunique answers together with the need for enormous amount of calculations are counted as the main challenges. To overcome such difficulties, a modified dimensional analysis method is proposed, which is able to reduce the number of dimensionless parameters. Another novel algorithm named “minimum resultant error method” is developed to provide proper criteria to investigate the compliance of the analytical results with empirical data. With this algorithm, yield stress, strain hardening exponent, and strain hardening coefficient are extracted as unique values by using a single indenter nanoindentation results. The simulation results are processed with combined modified dimensional analysis method and minimum resultant error method algorithms. The effects of interlayer, friction coefficient, and indenter tip radius are investigated. Error analysis to the modulus of elasticity is undertaken and the results show less than 2% error for the infimum point, while the individual dimensionless functions errors are below 3.4%. According to the results, this new approach is well-coped with the earlier studies.
“…A change in the indentation conditions allows a systematic study of the influence of various factors on the processes occurring in the contact zones of the materials. As a rule, the aim of works related to computer simulation of the material behavior under indentation is to study the mechanisms of plastic deformation in the zone of a spherical or pyramidal indenter, visualize defect structures, and interpret loadindentation curves [31][32][33][34]. Despite the high information content of such studies, it is difficult to analyze the results due to the complex deformation pattern.…”
Section: Peculiarities Of Plasticity Nucleation In Metals Under Nanoimentioning
The chapter is devoted to the analysis of the features of local structural rearrangementsin nanostructured materialsunder shear loadingand nanoindentation. The study was carried out using molecular dynamics-based computer simulation. In particular, we investigated the features of symmetric tilt grain boundary migration in bcc and fcc metals under shear loading. The main emphasis was on identifying atomic mechanisms responsible for the migration of symmetric tilt grain boundaries. We revealed that grain boundaries of this type can move with abnormally high velocities up to several hundred meters per second. The grain boundary velocity depends on the shear rate and grain boundary structure. It is important to note that the migration of grain boundary does not lead to the formation of structural defects. We showed that grain boundary moves in a pronounced jump-like manner as a result of a certain sequence of self-consistent displacements of grain boundary atomic planes and adjacent planes. The number of atomic planes involved in the migration process depends on the structure of the grain boundary. In the case of bcc vanadium, five planes participate in the migration of the Σ5(210)[001] grain boundary, and three planes determine the Σ5(310)[001] grain boundary motion. The Σ5(310)[001] grain boundary in fcc nickel moves as a result of rearrangements of six atomic planes. The stacking order of atomic planes participating in the grain boundary migration can change. A jump-like manner of grain boundary motion may be divided into two stages. The first stage is a long time interval of stress increase during shear loading. The grain boundary is motionless during this period and accumulates elastic strain energy. This is followed by the stage of jump-like grain boundary motion, which results in rapid stress drop. The related study was focused on understanding the atomic rearrangements responsible for the nucleation of plasticity near different crystallographic surfaces of fcc and bcc metals under nanoindentation. We showed that a wedge-shaped region, which consists of atoms with a changed symmetry of the nearest environment, is formed under the indentation of the (001) surface of the copper crystallite. Stacking faults arise in the (111) atomic planes of the contact zone under the indentation of the (011) surface. Their escape on the side free surface leads to a step formation. Indentation of the (111) surface is accompanied by nucleation of partial dislocations in the contact zone subsequent formation of nanotwins. The results of the nanoindentation of bcc iron bicrystal show that the grain boundary prevents the propagation of structural defects nucleated in the contact zone into the neighboring grain.
“…Inverse methods have been employed in many studies to characterise material behaviours using various testing techniques, such as micro-indentation tests [21,22], three-point bending (TPB) tests [23], and SPT tests [24]. One of the advantages of inverse methods is that it is easy to implement, even for investigators with limited theoretical knowledge of the testing techniques.…”
Section: Efforts Have Been Made By Researchers To Develop Miniaturisementioning
Small punch tensile (SPT) tests have been carried out for a CoNiCrAlY coating at room temperature (RT), 500°C and 700°C. Highly re-producible results have been obtained for SPT at 700°C while the formation of early cracking at lower temperatures tends to compromise the repeatability of the tests. An alternative novel miniature specimen testing method has been developed and used for the miniature tensile tests of the CoNiCrAlY coating in the same temperature range. Good agreements have been achieved between the SPT and miniature tensile testing results regarding the ductile to brittle transition temperature (DBTT). Excellent repeatability has been achieved over the full range of the temperature for the miniature tensile tests. An inverse approach has been developed and used to extract the mechanical properties of the material from the miniature tensile tests, using a temperature-dependent Johnson-Cook model. Finite element (FE) modelling of the SPT tests, including damage evolution, has been carried out using the extracted material properties to give comparable predictions of the SPT testing results, such as the loaddisplacement curves and the approximate locations of the fracture failures.
KeywordsCoNiCrAlY coating; miniature tensile test; small punch tensile test; high temperature properties; inverse method; ductile-to-brittle transition
Manuscript category SOLID MECHANICS
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